How do I know the minimum and maximum number in an array?

By Wayan in Core API, Util Package 0 Comment 
package org.kodejava.util;

import java.util.Arrays;
import java.util.Collections;

public class ArrayMinMax {
    public static void main(String[] args) {
        // Creates an array of integer numbers in it.
        Integer[] numbers = {8, 2, 6, 7, 0, 1, 4, 9, 5, 3};

        // To get the minimum or maximum value from the array we can
        // use the Collections.min() and Collections.max() methods.
        // But as this method requires a list type of data we need
        // to convert the array to list first.
        int min = Collections.min(Arrays.asList(numbers));
        int max = Collections.max(Arrays.asList(numbers));

        // Viola! we get the minimum and the maximum value from the
        // array.
        System.out.println("Min number: " + min);
        System.out.println("Max number: " + max);
    }
}

And here are the results:

Min number: 0
Max number: 9

How can I change file attribute to writable?

By Wayan in Core API, IO 0 Comment

Prior to Java 1.6 the java.io.File class doesn’t include a method to change a read only file attribute and make it writable. To do this on the old days we have to utilize or called operating system specific command. In Java 1.6 a new method named setWritable() was introduced to do exactly what the method name says.

package org.kodejava.io;

import java.io.File;

public class WritableExample {
    public static void main(String[] args) throws Exception {
        File file = new File("Writable.txt");

        // Create a file only if it doesn't exist.
        boolean created = file.createNewFile();

        // Set file attribute to read only so that it cannot be written
        boolean succeeded = file.setReadOnly();

        // We are using the canWrite() method to check whether we can
        // modified file content.
        if (file.canWrite()) {
            System.out.println("File is writable!");
        } else {
            System.out.println("File is in read only mode!");
        }

        // Now make our file writable
        succeeded = file.setWritable(true);

        // re-check the read-write status of file
        if (file.canWrite()) {
            System.out.println("File is writable!");
        } else {
            System.out.println("File is in read only mode!");
        }
    }
}

And here are the result of the code snippet above:

File is in read only mode!
File is writable!

How can I change file attribute to read only?

By Wayan in Core API, IO 0 Comment

This code demonstrate how we can modify file attribute to be read only. File class has a setReadOnly() method to make file read only and a canWrite() method to know whether it is writable or not.

package org.kodejava.io;

import java.io.File;

public class FileReadOnlyExample {
    public static void main(String[] args) throws Exception {
        File file = new File("ReadOnly.txt");

        // Create a file only if it doesn't exist.
        boolean created = file.createNewFile();

        // Set file attribute to read only so that it cannot be written
        boolean succeeded = file.setReadOnly();

        // We are using the canWrite() method to check whether we can
        // modified file content.
        if (file.canWrite()) {
            System.out.println("File is writable!");
        } else {
            System.out.println("File is in read only mode!");
        }
    }
}

This code snippet print the following output:

File is in read only mode!

How do I know the memory size in virtual machine?

By Wayan in Core API, Lang Package 0 Comment

If you want to know the free memory, and the total memory available in the Java runtime environment then you can use the following code snippet to check.

package org.kodejava.lang;

public class MemoryExample {
    public static void main(String[] args) {
        long freeMemory = Runtime.getRuntime().freeMemory();
        long totalMemory = Runtime.getRuntime().totalMemory();

        System.out.println("Free Memory  = " + freeMemory);
        System.out.println("Total Memory = " + totalMemory);
    }
}

Here is the result of the code snippet above:

Free Memory  = 1018439896
Total Memory = 1029177344

How do I ping a host?

By Wayan in Core API, Networking 0 Comment

Since Java 1.5 (Tiger) the java.net.InetAddress class introduces isReachable() method that can be used to ping or check if the address specified by the InetAddress is reachable.

package org.kodejava.net;

import java.net.InetAddress;

public class PingExample {
    public static void main(String[] args) {
        try {
            InetAddress address = InetAddress.getByName("172.16.2.0");

            // Try to reach the specified address within the timeout
            // period. If during this period the address cannot be
            // reach then the method returns false.
            boolean reachable = address.isReachable(10000);

            System.out.println("Is host reachable? " + reachable);
        } catch (Exception e) {
            e.printStackTrace();
        }
    }
}